Who s afraid of freeform optics? * Webinar 17 January 2018

Transcription

1 Who s afraid of freeform optics? * Webinar 17 January 2018

2 Outline About the presenters Spectrum Scientific, Inc. (SSI) Challenges of using freeform optics How to use freeform optics Low cost replicas from complex components Advantages of the replication process Introduction to freeform optics Benefits of utilizing freeform optics Freeform surface design in OpticStudio Manufacturability Metrology Transitioning into manufacturing Assembly considerations

3 Presenters Introduction Spectrum Scientific Daphnie Chakran President & CEO Spectrum Scientific Presenter Zemax Erin Elliott Optical Research & Prototyping Engineer Zemax Presenter David Cook General Manager Spectrum Scientific Q&A Dave Erickson CTO Spectrum Scientific

4 Spectrum Scientific, Inc. Spectrum Scientific, Inc. (SSI) was established in 2004 Space qualified Clean room facility ISO 9001:2015 certified In-house capabilities o Manufacturing o Design o Coating o System Assembly o Engineering o Precision Metrology

5 Spectrum Scientific, Inc. Capabilities Spherical mirrors Aspheric mirrors Freeform mirrors Off-axis parabolic mirrors Ellipsoidal mirrors Holographic diffraction gratings Hollow retroreflectors UV spectrometers

6 Challenges of using freeform optics Understanding & Visualization Designing & Specifying for Manufacturability Cost Assembling your Freeform Measurement

7 How to use freeform optics Add Replace Redo

8 Low cost replicas from complex components Precision Machining Expensive Polishing Fixtures Expensive Polishing & Metrology Processes Expensive Original

9 Advantages of the replication process Replication is the most cost effective method for high volume applications Spectrum Scientific s replication process delivers: High fidelity reflective aspheric mirrors λ/10 reflective optics High volume production of freeform mirrors at a reasonable cost and with high repeatability

10 Advantages of the replication process Exceptional quality surfaces are faithfully replicated to very high fidelity o Component figure: macroscopic scale o Scratches and digs; microscopic scale o surface roughness: sub nanometer scale. Mounting features can be easily incorporated into the component Master optic Thin film coating Replicated mirror Greater design flexibility UV, VIS, IR coatings Lower OEM cost than conventional polishing and/or diamond machining Release agent Polymer layer

11 Introduction to freeform optics Definition of freeform: A curved optic without axial symmetry Flat & Spherical optics 1 Introduction of commercially available aspheric optics 3 Deterministic freeform manufacturing methods (DT & MRF) 1 High precision, state of the art freeform manufacturing 1900s 1950s 1970s 2000s 2010s Initial freeform designs 2 Significant commercial freeform manufacturing: Polaroid SX-703, 4, 5 Mainstream systems integrate freeforms into production (Beam Shaping, HUDs, VR/AR) 6

12 Benefits of utilizing freeform optics Single optical surface allowing for compound compensation Improved system performance Redistribution of tolerances in the system design Reduces the number of optics Additional aberration correction The SCUBA-2 telescope 3, 5, 7

13 System design - freeform benefit example Offner baseline all-spherical design Offner compact freeform design 8 Overall volume decreased from 530 cm 3 to 100 cm 3 Reimers, Jacob, et al. "Increased Compactness of an Imaging Spectrometer Enabled by Freeform Surfaces." International Optical Design Conference. Optical Society of America, 2017.

14 Freeform tools in OpticStudio Surfaces in sequential mode Standard surfaces allow a ROC and conic constant. Biconic surfaces allow separate ROCs and conics in X and Y. Toroidal, superconic Even Asphere, Extended Asphere, Odd Asphere, Extended Odd Asphere, Q-type Aspheres, Alternate Even/Odd Asphere Zernike Standard Phase/Sag, Zernike Fringe Phase/Sag, Biconic Zernike Polynomial, Extended Polynomial, Chebyshev Polynomial Grid Phase/Sag Analysis tools ISO Element drawings Surface and curvature tables and cross-sections Power as a function of pupil coordinate, field angle Universal plots Optimization tools FTLT/FTGT full thickness less than and greater than POWF Power at a given field point POWP Power at a given point in the pupil BFSD Best fit sphere data SCUR Surface curvature at a given X and Y coordinate SDRV Derivative of the sag at a given X and Y coordinate

15 Optimizing with freeforms in OpticStudio Three Mirror Anastigmat example Traditionally done with decentered conics. With freeforms, can mimic those shapes with on-axis parts. But, freeforms open up the design space beyond the traditional conics. Design with freeforms requires caution! Optimization has many more parameters available. Typically need to reduce the # of parameters in an intelligent way. Never use terms that violate the symmetry of the system. TMA has symmetry about the YZ plane, so terms that are odd in X are disallowed. Start with lowest-order term power by connecting X and Y radii. Then, release to allow astigmatism, then coma, etc. Always include at least a very small field angle. Easy to create systems that are perfect at one field point. Never turn all the terms on to see what happens! Never keep a term that doesn t improve the performance!

16 Optical Testing of Freeforms OpticStudio can be used to model the optical test setup for each freeform. The test method sets the maximum slope limitation for the freeform part. Typical optical testing methods: Interferometric testing (unassisted): For freeforms without large departure from spherical surfaces. Max. slope of the freeform part is limited by the resolution of the interferometer. Interferometric testing with a null lens: Removes part of the wavefront departure so that the interferometer can resolve the fringes. Null lens must be designed for precision manufacture, so can t be too complex. Max. slope of the freeform part is limited by the precision required for the null lens. Interferometric testing with a CGH: Also removes part of the wavefront departure. Max. slope of the freeform part is limited by the resolution of the CGH.

17 Manufacturability Manufacturing Methods Originals by direct manufacturing Copies from masters (injection molding, pressed glass, nano-imprint lithography) Large volume, repeatable process using the SSI replication process Superior stray light performance from replicated mirror compared to diamond machined mirror

18 Metrology Measurements down to a nm-scale Wide range of contact & non-contact measurement methods o Contact - common, slow µm-scale o Non-contact - higher precision 9

19 Transitioning Into manufacturing Communication with the manufacturer is critical Specifying the optical surface o Surface equation o Sag table Additional parameters to consider o Surface profile (figure error) o Micro-surface roughness (RMS) o Mid-spatial frequency (slope errors) 11 Surface Equation 10

20 Assemble your instrument Alignment considerations for optic manufacturing and system integration

21 Summary Nobody should be afraid of freeform optics* They can offer significant benefits and cost savings in modern optical systems Thank You This is an exciting time in our industry Freeforms have the potential revolutionize a lot of different markets *with apologies to Edward Albee

22 References 1. Thompson, Kevin P., and Jannick P. Rolland. "Freeform optical surfaces: a revolution in imaging optical design. Optics and Photonics News 23.6 (2012): Kanolt, Clarence W. "Multifocal ophthalmic lenses. U.S. Patent No. 2,878, Mar Fang, F. Z., et al. "Manufacturing and measurement of freeform optics. CIRP Annals-Manufacturing Technology 62.2 (2013): Plummer, William T. "Free-form optical components in some early commercial products." Proc. SPIE. Vol Henselmans, Rens. "Non-contact measurement machine for freeform optics." Macromolecules 35 (2009): Cakmakci, Ozan, and Jannick Rolland. "Head-worn displays: a review." Journal of display technology 2.3 (2006): Hoogstrate, André M., et al. "Manufacturing of high precision aspherical and freeform optics." Proc. SPIE. Vol Interferometric Measurement of Mid-Spatial Frequency Wavefront Errors, Smythe, Aikens, IODC Denver June Reimers, Jacob, et al. "Increased Compactness of an Imaging Spectrometer Enabled by Freeform Surfaces." International Optical Design Conference. Optical Society of America, Non-contact measurement of optical freeforms current solutions and advantages, F. Reischer, S. Mühlig, E. Grüner, J. Siepmann, S. Mika, A. Beutler, M. Lotz, A. Wiegmann, Mahr GmbH. Laser World of Photonics, June Zemax, LLC. OpticStudio 16 SP2 Help Files." OpticStudio 16 SP2. (2016): 476. Print. 11. ISO

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